Vehicle safety belts typically include a retractor mechanism which causes the belt to automatically wind onto a spring loaded reel when not in use. The retractor also insures that the belt remains flush against the person's body as the person changes seated positions, thus allowing the person to move freely without having to manually adjust the belt. In order to secure the person in the event of an emergency, the retractor also has a locking mechanism which senses the emergency condition and locks the reel, thus preventing further extension of the belt and keeping the person secured against the seat.
Typically a retractor responds in an emergency situation by sensing the deceleration of the vehicle, or the rotational acceleration of the reel. In an example of an acceleration sensing mechanism a freely rotating inertia element senses the belt unwinding, angular acceleration of the reel. As the reel accelerates, the rotation of the inertia element lags behind the rotation of the reel assembly. The relative change in position causes the inertia element to move a locking or braking mechanism into position and brake the reel. Some retractors, have locking means which respond to both the acceleration of the belt and the deceleration of the vehicle.
The locking mechanism in some prior art involves a ratchet attached to one or both sides of the reel which is surrounded by teeth. There is also either a bar or a pawl which is capable of locking the reel by engaging the ratchet teeth, and which moves into this locking position upon sensing the emergency condition. The ratchet teeth may be located either on the radial interior or exterior relative to the retractor housing. That is, the ratchet may be designed as a wheel with teeth pointing outward on the outside of the wheel or as a ring with teeth pointing inward on the inner circumference of the ring. Inwardly extending teeth or locking elements offer certain advantages, but such systems have other complexities concerning the mounting of components.
Thus it is desirable that the retractor have a minimum number of parts, be compact and of course be reliable and inexpensive. In this regard it is desirable to eliminate parts by having some elements perform dual functions. One example of this is to have reel locking holes formed in a reel frame rather than a separate element. In one such arrangement, a rotating inertia mass having axially extending teeth or lugs is moved axially in response to a predetermined acceleration causing the teeth to enter locking holes in the frame. In some instances, the locking teeth may only partially move into the locking holes while the inertia mass is still rotating at a significant velocity such that the inertia mass may not be immediately stopped, and the tips of the teeth may be damaged. Thus a need exists to insure that the teeth are always properly aligned when the inertia mass is moved axially to enter the locking holes. U.S. Pat. No. 3,979,083-Fohl discloses one such arrangement, but it is somewhat complex and a simplified arrangement is desired.